1. Field of the Invention
The invention relates to method and apparatus for determining elastic constants in metals, and in particular in metal tubes.
2. Description of the Prior Art
Coriolis mass flow rate meters are used to measure the mass flow of a process fluid. As disclosed in the art, such as in U.S. Pat. No. 4,491,025, issued to J. E. Smith et al. on Jan. 1, 1985, one typical type of Coriolis mass flow rate meter contains two parallel flow conduits, each typically being a U-shaped metal tube. Each metal tube is driven to oscillate about an axis to create a rotational frame of reference. For such a U-shaped metal tube, this axis can be termed the bending axis. As process fluid flows through each oscillating metal tube, movement of the fluid produces reactionary Coriolis forces that are perpendicularly oriented to both the velocity of the fluid and the angular velocity of tube. These reactionary Coriolis forces cause each tube to twist about a torsional axis, that for a U-shaped metal tube, is normal to its bending axis. The amount of twist is proportional to the mass flow rate of the process fluid that flows through the tube.
In practice, the above-described Coriolis mass flow rate meters often required a zero-level offset adjustment. This offset adjustment properly calibrates the meter by reducing the measured mass flow rate to zero when no fluid flows through the meter. Further, it has been found that in manufacturing these meters the zero-level offset adjustment value can be large in many cases and, in addition, fluctuate between various values when the meter is in use. The source of this large zero-level offset adjustment value and its fluctuation has not been recognized in the prior art.
In light of this, a need exists to determine the cause of the large zero-level offset adjustment values and the fluctuation thereof in order to provide more reliable and accurate Coriolis mass flow rate meters than has been heretofore possible.